Field of the Disclosure
Embodiments generally relate to input sensing and, in particular, to input sensing by driving sensor electrodes for proximity sensing.
Description of the Related Art
Input devices including proximity sensor devices (also commonly called touchpads or touch sensor devices) are widely used in a variety of electronic systems. A proximity sensor device typically includes a sensing region, often demarked by a surface, in which the proximity sensor device determines the presence, location, and/or motion of one or more input objects. Input objects can be at or near the surface of the proximity sensor device (“touch sensing”) or hovering over the surface of the proximity sensor device (“proximity sensing” or “hover sensing”). Proximity sensor devices may be used to provide interfaces for the electronic system. For example, proximity sensor devices are often used as input devices for larger computing systems (such as touchpads integrated in, or peripheral to, notebook or desktop computers). Proximity sensor devices are also often used in smaller computing systems (such as touch screens integrated in cellular phones or tablet computers).
Proximity sensor devices can measure changes in mutual capacitance (or “transcapacitance”) relating to the presence of an input object in a sensing region of the sensor device. Given an array of sensing regions, transcapacitance sensing can be used to generate a capacitive image, from which one or more input objects can be resolved at a given time. However, transcapacitance can produce less reliable results as the distance between the input objects and the proximity sensor device surface increases (e.g., proximity or hover sensing).
As an alternative to transcapacitance, proximity sensor devices can measure changes in self capacitance (or “absolute capacitance”) relating to the presence of an input object in a sensing region. Sensing changes in absolute capacitance offers better proximity sensing than sensing changes in transcapacitance. Parasitic capacitances, however, limit the ability of the proximity sensor device to detect changes in absolute capacitance. If left uncontrolled, parasitic capacitances can cause significant signal loss, limiting the reliable distance in which the proximity sensor device can detect proximate object(s).